It is known that there are enzymes which catalyze the oxidation of alcohols and aldehydes to aldehydes and carboxylic acids, respectively, and have pyrroloquinoline quinone ("PQQ") as a prosthetic group.
Methanol dehydrogenases, which are members of alcohol dehydro-genases, catalyze not only the oxidation of methanol to aldehyde, but also formaldehyde to formic acid and formate (Advances in Microbial Physiology, 27, 113-209, 1986). These methanol dehydrogenases oxidize a wide range of primary alcohols, such as methanol and ethanol and some aldehydes but most of these enzymes cannot oxidize secondary alcohols. The methanol dehydrogenases derived from Methylobacterium organophilum, Pseudomonas C, Diplococcus PAR, and Rhodopseudomonas acidophile are examples of dehydrogenases which can catalyze the oxidation of secondary alcohols. To carry out the oxidation of alcohols and aldehydes, the methanol dehydrogenases use activators, such as methylamine or ammonia.
Quinoprotein alcohol dehydrogenase from Pseudomonas aeruginosa (Biochem. J., 223, 921-924, 1984) and quinohaemprotein alcohol dehydrogenase from Pseudomonas testosteroni (Biochem., J., 234, 611-615, 1986) are other examples of alcohol dehydrogenases having PQQ as a prosthetic group. The former enzyme is a monomer whose molecular weight is 101,000 and requires ammonium salts or amines as activators. The latter enzyme is a monomer, whose molecular weight is about 67,000, and contains one haem c group in its molecule.